1. Field of the Invention
The present invention relates to a hydraulic control device for an automatic transmission of a vehicle, and particularly, the present invention relates to a hydraulic control device for an automatic transmission that corrects engagement control oil pressure at in-gear control if necessary.
2. Description of the Related Art
Heretofore, a setup of engagement control oil pressure for a clutch at in-gear control is carried out so as to meet certain standards for features (setup conditions) of a hydraulic control device for an automatic transmission. The setup conditions include: variation in an oil pressure characteristic to current of a linear solenoid valve for regulating oil pressure (line pressure) of hydraulic oil; a clutch clearance (aged deterioration of the clutch); a possibility to cause shock of clutch engagement to occur at a change of the oil pressure characteristic due to a difference (change) in an environment such as temperature of AT fluid oil; time until the clutch engages; and the like.
A method of controlling a regulating section of the hydraulic control device is known in order to suppress influence of variation in the oil pressure characteristic to current due to individual variability of linear solenoid valves particularly of the setup conditions as described above (see Japanese Patent Application Publication No. 2006-125435, for example; hereinafter, referred to as “Patent Document 1”). In this method, characteristic values of output oil pressure such as original oil pressure and oil temperature to a command value of the output oil pressure of the linear solenoid valve are actually measured in advance; the characteristic values are stored in a memory of an electronic control unit; and the regulating section of the hydraulic control device is controlled by reading out the characteristic values from the memory.
In the hydraulic control device for the automatic transmission disclosed in Patent Document 1, the characteristic values of the output oil pressure thus actually measured are encoded with a two-dimensional code such as a bar code, and it is attached (or applied) to a surface of the transmission. Then, in a manufacturing process of a vehicle, this two-dimensional code is read out to store the characteristic values in the memory. By carrying out a setup of the engagement control oil pressure on the basis of the characteristic values, it is possible to suppress influence of variation in the oil pressure characteristic to current due to individual variability of linear solenoid valves.
However, in the hydraulic control device for the automatic transmission disclosed in Patent Document 1, the influence of the variation in the oil pressure characteristic to current of the linear solenoid valves can be suppressed effectively, but in the hydraulic control device for the automatic transmission, it needs a step of actually measuring the above characteristic values in advance, a step of encoding them into a two-dimensional code, and a step of reading out this two-dimensional code to store it in a memory in a manufacturing process of a vehicle. Therefore, there has been a problem that it is complicated to carry out such steps for the linear solenoid valve used in the regulating section of the hydraulic control device for the automatic transmission, and this causes manufacturing costs of the vehicle to be increased.
Further, by carrying out control of regulation in the hydraulic control device for the automatic transmission using the above characteristic values, it is possible to heighten setup accuracy of original oil pressure and output oil pressure to oil temperature, but there has been a problem that it is impossible to improve resistance (toughness) against a change in a state of the automatic transmission such as deteriorated state (aged deterioration) due to abrasion of a clutch disk.
In the case where a transmission (automatic transmission) provided with a linear solenoid valve whose variation in an oil pressure characteristic to current is large is applied to a vehicle sensitive to shock (in particular, a saloon car (sedan type of vehicle) in which vehicle weight to output of an engine is light), in-gear control for a clutch must be set up in consideration of a change in a state such as temperature change and a deteriorated state. In the case where it takes much time until the clutch engages or there is a region in which shock at clutch engagement cannot be absorbed, squat in-gear control in which clutches of a low gear and higher gear are caused to engage with together, and the like have been utilized. However, there has been a problem that in the squat in-gear control, since it is necessary to operate two clutches, not only there is a possibility to be affected by the variation in the oil pressure characteristic to current, but also a usable temperature range for the squat in-gear control is limited.